Thermal capacitor for increasing energy efficiency

ABSTRACT

An apparatus that increases energy efficiency by insulating a refrigerator or freezer wall is disclosed. The apparatus includes an inner wall made of stainless steel or aluminum and an exterior wall. A backing sheet with a series of cells is attached to the inner wall. The cells are filled with a gel that is formed by combining a super-absorbent cross-linked sodium polymer with water. The gel is has a ratio of 3 ounces of polymer to every 4 gallons of water. Finally, a layer of insulating foam interposed between the cells and the outer wall.

FIELD OF THE INVENTION

The invention relates generally to insulation materials. More specifically, the invention relates to a thermal capacitor that increases energy efficiency of refrigeration and freezer units.

BACKGROUND ART

For refrigerators, freezers and other similar devices, maintaining a designated target temperature is critical to their operation. The designated target temperature is usually set through a thermostat and maintained by cycling on and off a compressor system to maintain the temperature. However, compressor systems consume a great deal of energy and their operation can be quite expensive. Therefore, it would be advantageous to increase energy efficiency by reducing the need to cycle a compressor system for a refrigerator or freezer.

SUMMARY OF THE INVENTION

In some aspects, the invention relates to an apparatus for insulating a wall comprising: an inner wall made of stainless steel or aluminum; an outer wall; a backing sheet attached to the inner wall; a series of cells attached to the backing sheet; a gel that is formed by combining a super-absorbent cross-linked sodium polymer with water in a ratio of 3 ounces of polymer to every 4 gallons of water, where the gel is located within each cell; and a layer of insulating foam interposed between the thermal capacitor and the outer wall.

In other aspects, the invention relates to an insulating wall comprising: an inner wall made of a thermally conducting material; an outer wall; a thermal capacitor in contact with the inner wall; and a layer of thermally insulating gel material interposed between the thermal capacitor and the outer wall.

In other aspects, the invention relates to an apparatus for a insulating a thermal storage device comprising: a closed container made of a thermally conducting metal material; and a thermally absorbent gel material enclosed within the container.

Other aspects and advantages of the invention will be apparent from the following description and the appended claims.

BRIEF DESCRIPTION OF DRAWINGS

It should be noted that identical features in different drawings are shown with the same reference numeral.

FIG. 1 shows an individual thermal capacitor cell in accordance with one embodiment of the present invention.

FIG. 2 shows a sheet of thermal capacitor cells in accordance with one embodiment of the present invention.

FIG. 3 shows a wall panel configuration in accordance with one embodiment of the present invention.

FIG. 4 shows a tube configuration in accordance with one embodiment of the present invention.

DETAILED DESCRIPTION

A thermal capacitor for increasing the energy efficiency of refrigerators, freezers and similar devices has been developed. The thermal capacitor assists in cooling and/or freezing in such devices and consequently reduces the energy required during operation. The reduction in energy consumption occurs by keeping the interior of the refrigeration/freezer unit cooler and thereby reducing the frequency of cycling the compressor.

FIG. 1 shows an individual thermal capacitor cell 10 in accordance with one embodiment of the present invention. The cell 10 includes an outer surface 12 and a backing 14. A thermally insulating gel material 16 (hereafter “gel”) is present inside the cell 10. The gel is formed by combining a super-absorbent cross-linked sodium polymer with water in a ratio of 3 ounces of polymer to every 4 gallons of water.

FIG. 2 shows a sheet of thermal capacitor cells 20 in accordance with another embodiment of the present invention. In this embodiment, the cells 10 are formed on a sheet of backing material 14. This forms a blanket of cells in a similar configuration to a “bubble wrap” type packing material. FIG. 3 shows a wall panel configuration in accordance with another embodiment of the present invention. The wall panel includes an inner wall 30 which faces the interior of the refrigerator or freezer unit. Next to the inner wall 30 is a sheet of thermal capacitor cells 20 with the backing 14 placed against the inner wall 30. Next, a layer of insulating material 32 such as foam is adjacent to the sheet of cells 20. Finally an outer wall 34 is present. The walls are typically made of metal such as stainless steel or aluminum because of their strength as well as their thermal conductivity properties.

The wall panel provides two functions for a refrigeration/freezer unit: a heat sink that removes heat from the interior of the unit; and a thermal capacitor that stores cold energy. With respect to the heat sink, the second law of thermodynamics is an axiom of thermodynamics concerning heat, entropy, and the direction in which thermodynamic processes can occur. In its simplest formulation, the second law states that heat will not spontaneously flow from a material at lower temperature to a material at higher temperature. Instead, heat will flow from a material at higher temperature to a material of lower temperature.

In the wall panel shown in FIG. 3, the gel inside the panel is cooled to a very low temperature over time by the refrigeration/freezer unit. Once it is cold, the sheet of cells makes the inner wall colder through physical contact which in turn makes the inner wall more attractive to heat inside the unit. The heat is drawn away from the interior of the unit and into the panel. This functions to make the interior of the unit colder and consequently requires less work from the compressor system. The gel in the cells of the sheet functions as a thermal capacitor that stores cold energy and cools the inner wall of the panel.

It should be understood that different embodiments of the present invention could vary in size, design and materials used. For example, the panel shown in FIG. 3 could be built as a wall panel of a refrigeration/freezer unit. In an alternative configuration, the panel could be an “add on” that is retrofitted to an existing unit. In another embodiment, the “cells” could be replaced by multiple metal tubes arranged in parallel with the gel inside. This would be configured in a similar fashion to a radiator.

FIG. 4 shows another example of a thermal storage vessel. This example is a hollow metal tube 40 that is filled with gel 42. In this example, the tube 40 is 3 inches in diameter and may be between 4-20 feet long. Also in this example, the metal is 20 gauge 304 stainless steel. In should be understood that these dimensions and materials may vary with alternative embodiments. When the metal tube is cooled, the gel inside draws the cold in through the metal and lowers the temperature of the gel as previously described.

As shown in FIG. 4, the tube is only filled to approximately 75% of its volume when the gel is warm or “discharged”. When the gel is frozen or “charged”, the gel expands to fill the rest of the volume of the tube. The tube has been tested in the temperature range from +40° F. to −80° F. The present invention has an approximate 3 day break-in period and then may be fully charged and ready for operation. Depending on room conditions, it typically takes 4 to 6 hours for the tubes to discharge

The tube embodiment may be used in a wide range of applications as described previously such as a retrofit device where a series of tubes are added to a freezer/refrigerator wall or the tubes may be built into the wall in a similar manner to the sheet of cells shown in FIG. 3. The advantage to the end-user is a more efficient operation and reduce energy costs when the cold thermal storage vessels are allowed to discharge.

Further enhancement of the invention will allow even more energy savings by using the compressor and fan assembly used by a refrigerator/freezer to power the compressor to charge the thermal storage vessels. A wind turbine is used to capture the wind energy that is displaced by the cooling fan on the condensing unit of the refrigerator/freezer. The wind turbine generates electricity that can be used to run the compressor to charge the thermal storage vessels. converted to energy to be used at that moment and or to charge the batteries. The airflow from numerous fans, the displaced are is moving at 24-28 mph. With proper fan blade design, this could result in 2000 watts per hour per fan. Additionally, any excess electricity cold be returned to the power grid for other uses. The use of a wind turbine on a compressor fan could have other uses to generate electricity in both industrial and residential applications without necessarily charging a thermal storage vessel. Additionally, such wind turbines could be used to generate power that charges thermal storage vessels in refrigerated tractor trailers. Instead of the compressor fan, the wind turbine could be attached to the exterior of the trailer to collect wind energy as the trailer moves down the highway.

The primarily focus of the present invention is the gel mixture inside of the metal resulting in the heat exchange opportunity and the cold thermal storage. The advantage to the end-user, is a more efficient operation and reduce energy costs when the cold thermal batteries are allowed to discharge.

While the invention has been described with respect to a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments can be devised which do not depart from the scope of the invention as disclosed here. Accordingly, the scope of the invention should be limited only by the attached claims. 

1. An apparatus thermal storage device, comprising: a hollow tube comprising 20 gauge 304 stainless steel, where the tube is about 4 feet in length and has a diameter of about 3 inches; and a gel that is formed by combining a super-absorbent cross-linked sodium polymer with water in a ratio of 3 ounces of polymer to every 4 gallons of water, where the gel fills the hollow tube to 75% of its volume when the gel is in a thermally discharged state.
 2. An apparatus for insulating a wall comprising: an inner wall made of stainless steel or aluminum; an outer wall; a backing sheet attached to the inner wall; a series of cells attached to the backing sheet; a gel that is formed by combining a super-absorbent cross-linked sodium polymer with water in a ratio of 3 ounces of polymer to every 4 gallons of water, where the gel is located within each cell; and a layer of insulating foam interposed between the series of cells and the outer wall.
 3. An insulating wall comprising: an inner wall made of a thermally conducting material; an outer wall; a thermal capacitor in contact with the inner wall; and a layer of thermally insulating gel material interposed between the thermal capacitor and the outer wall.
 4. The insulating wall of claim 3, where the thermal capacitor comprises: a backing sheet; a series of thermal storage cells attached to the backing sheet; and a thermally absorbent gel material within each thermal storage cell.
 5. The insulating wall of claim 4, where the thermally absorbent gel material comprises a gel formed by combining water with a super-absorbent polymer.
 6. The insulating wall of claim 5, where the gel is formed by combining super-absorbent cross-linked sodium polymer with water in a ratio of 3 ounces of polymer to 4 gallons of water.
 7. An apparatus for a insulating a thermal storage device comprising: a closed container made of a thermally conducting metal material; and a thermally absorbent gel material enclosed within the container.
 8. The apparatus of claim 7, where the metal material is stainless steel.
 9. The apparatus of claim 7, where the metal material is aluminum.
 10. The apparatus of claim 7, where the absorbent material is a gel made by absorbing water into a super absorbent polymer.
 11. The apparatus of claim 10, in which the super absorbent polymer comprises a cross-linked sodium polymer.
 12. A thermal storage device comprising: a hollow metal tube; and a gel that is formed by combining a super-absorbent cross-linked sodium polymer with water in a ratio of 3 ounces of polymer to every 4 gallons of water, where the gel fills the hollow metal tube to 75% of its volume when the gel is in a thermally discharged state.
 13. The device of claim 12, where the metal tube comprises 20 gauge 304 stainless steel.
 14. The device of claim 12, where the metal tube has a diameter of about 3 inches.
 15. The device of claim 12, where the metal tube has a length between 4-20 feet. 